They have code readers at any car part store that will tell you what the service engine light means there are over 200 codes. I got my code reader at wal-mart there about $20-25. you can also go to auto zone or places like that and they'll tell ya what the service engine light is sayin for free. If you have any other questions just ask.

Take a paper clip, and bend it into a "U", then plug the two ends into the top right ports on your ALDL connection, which should be below and left of the steering column on the bottom of the dash.
Here's what it will look like, and the ports you want to plug the clip into are the A and B.

And here's how to read the light for codes and this will tell you if there is a fault, and the code will tell you what circuit the fault is in.
To do a diagnostic on engine codes you take a paper clip and connect terminal (A) and (B) together. A Code 12 will flash on the Check Engine light 3 times first and then give you any additional codes if present. A code is displayed for example 12 (1 flash, pause, 2 flashes). Listed below is a list of all the available codes and what they mean.
Trouble Codes Circuit or System Probable Cause
Code 12 No distributor reference
pulses to the ECM This code will flash whenever the diagnostic terminal is grounded with the ignition turned On and the engine not running. If additional trouble codes are stored in the ECM then they will appear after this code has flashed 3 times. If this code appears while the engine is running, no reference pulses from the distributor are reaching the ECM.
Code 13 Oxygen sensor circuit Check for a sticking or misadjusted throttle position sensor. Check the wiring and connectors from the oxygen sensor. Replace the oxygen sensor.
Code 14 Coolant sensor/High temp If the engine is experiencing overheating problems the problem must be rectified before continuing. Check all wiring and connector associated with the coolant temperature sensor. Replace the coolant temperature sensor.
Code 15 Coolant sensor/Low temp See Above, then check the wiring connections at the ECM.
Code 21 Throttle position sensor/
voltage high Check for a sticking or misadjusted TPS plunger. Check all wiring and connections between the TPS and the ECM. Adjust or replace the TPS. (see other instructions on doing this)
Code 22 Throttle position sensor/
voltage low Check TPS adjustment. Check the ECM connector. Replace the TPS.
Code 23 MAT low temp indication Sets if the Manifold Air Temperature (MAT) sensor, connections or wires are open for 3 seconds.
Code 24 Vehicle speed sensor A fault in this circuit should be indicated only when the vehicle is in motion. Disregard if it is set when the drive wheels are not turning. Check the connections at the ECM. Check the TPS setting.
Code 25 ATI sensor/high air High temperature indication. Sets if the sensor or signal line becomes grounded for 3 seconds.
Code 31 Wastegate Overboost
Code 32 EGR Vacuum switch shortened to ground on start-up, switch not closed after the ECM has commanded the EGR for a specified period of time or the EGR solenoid circuit is open for a specified period of time. Replace the EGR valve.
Code 33 MAP sensor Check the vacuum hoses from the MAP sensor. Check the electrical connections at the ECM. Replace MAP sensor.
Code 34 Vacuum sensor or
MAP sensor This will set when the signal voltage from the MAP sensor is too low. Instead the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery. Replace the MAP sensor.
Code 35 IAC valve Idle Air Control error. Code will set when closed throttle speed is 50 rpm above or below the correct idle speed for 30 seconds. Replace the IAC.
Code 42 Electronic Spark Timing
(EST) This code is when this circuit is grounded or open. A malfunctioning HEI module can cause this code.
Code 43 Electronic Spark Control
(ESC) The ESC retard signal has been on for too long or the system has failed a functional check.
Code 44 O2/Lean exhaust Check the ECM wiring connections, particularly terminals 8 and 15. Check for vacuum leakage at the TBI base gasket, vacuum hoses or the intake manifold gasket. Replace the oxygen sensor.
Code 45 O2/Rich exhaust Check the evaporative charcoal canister and its components for the presence of fuel. Replace the oxygen sensor.
Code 51 PROM or MEM-CAL Make sure the PROM or MEM-CAL is properly installed in the ECM. Replace the PROM or MEM-CAL.
Code 52 CALPAK Check the CALPAK to insure proper installation. Replace the CALPAK.
Code 53 System over-voltage (indicates a basic alternator problem) Check charging system.
Code 54 Fuel Pump Low fuel pump voltage. Sets when the fuel pump voltage is less than 2 volts when reference pulses are being received.
Code 55 ECM Be sure that the ECM ground connections are tight. If they are, replace the ECM.

"it could be as simple as a loose gas cap"
Sorry, on an older vehicle there is no LDP (leak detection pump) which checks for leaking gasoline vapors. These only came out in the late 90's. I want to say either 96 or 98? I forget which. /forums/images/graemlins/burb.gif

Useful Searches

>
About Us>
>
In May of 1999 CK5 started out as a tribute to America's favorite 4x4 utility truck. Since then it has grown to be
a leader among full size Chevrolet K5 Blazer and GMC Jimmy web sites across the Internet. CK5 has since expanded
to include the C/K series GM Truck and Suburban as well as past and present GM models.
>>
With its technical articles, factory specifications, photo gallery, classifieds, active message forum, product
reviews and original automotive content it's an unbeatable source.